KE2: Start working on KtTypes

[igfoo]

This adds the beginning of KtType extraction.

The main change is in the dbscheme relations, which now look like:

/**
 * `id` is the Kotlin type for the non-nullable class type `classid`.
 */
kt_class_types(
  unique int id: @kt_class_type,
  int classid: @reftype ref
)

/**
 * `id` is the Kotlin type that is the same as `kttypeid`, but is nullable.
 */
kt_nullable_types(
  unique int id: @kt_nullable_type,
  int kttypeid: @kt_type ref
)

/**
 * `id` is the Kotlin type that is the alias called `name` of `kttypeid`.
 * That is, it has been defined by `typealias name = kttypeid`.
 */
kt_type_alias(
  unique int id: @kt_type_alias,
  string name: string ref,
  int kttypeid: @kt_type ref
)

and useType now produces these.

This broke the KE1 build, which for now I've just fixed with TODO() calls; I think it makes sense to fix this properly later, once we are confident that this is the right way to go.

fakeKotlinType is now gone; we should make proper Kotlin types in cases where we used to use it.

[tamasvajk]

Minor: We typically have a ; separator between parts of the label. So I think this should be "@\"kt_class;{$classId}\""

[tamasvajk]

Is this correct? Shouldn't we check the nullability of the KaClassType?

[igfoo]

Ah, the nullability belongs in useType, but it looks like that I got so focused on working out what the dbscheme tables should look like that I didn't add it. I'll add a commit for that.